Mueller matrix measurement system and measurement method

Abstract

A Mueller matrix measurement system and a measurement method belong to the field of polarization detection technology, and solve the problem of how to quickly and completely measure the Mueller matrix of a sample. A light source emits modulated light vertically upward, and a first vertical linear polarizer is used to convert the incident modulated light into linearly polarized light; a first phase delay plate and a second phase delay plate modulate the polarization state of the linearly polarized light, a digital micro-reflector is loaded with a stripe image, and the linearly polarized light with the stripe image is scattered in a biological tissue to be measured, and the scattered light passes through a third phase delay plate, a first phase delay plate, and a second vertical linear polarizer in sequence and is captured by a camera; the polarization state of the modulated linearly polarized light is controlled by the first phase delay plate, the second phase delay plate, the third phase delay plate, and the fourth phase delay plate to control the measurement depth of the polarized light to the biological tissue to be measured, and the polarization states of 16 polarized lights are modulated in total, thereby improving the calculation accuracy of the light intensity value of the emergent light, and being able to calculate the complete Mueller matrix of the sample.

Description

Technical Field

[0001] The invention belongs to the technical field of polarization detection and relates to a Mueller matrix measurement system and a measurement method. Background Art

[0002] Biological tissues carry a wealth of optical information (such as transmission, reflection, attenuation information, delay information, and depolarization information), which can reflect the physiological characteristics related to biological tissues. For example, general pathological tissues (such as cancer) have their highly organized microstructures destroyed and the inherent heterogeneity of tissue morphology is lost, thus better retaining the polarization state of the probe light and having lower depolarization. Scar tissue contains dense collagen fibers, and the probe light beam undergoes more orthogonal polarization state phase shifts when propagating in the tissue sample, thus having high linear delay. Abnormal changes in the biological tissue matrix (such as collagen remodeling) lead to changes in its tissue scattering and absorption characteristics, thereby changing the depolarization characteristics of the tissue.

[0003] The Stokes vector is used to define the polarization state of light, and the Mueller matrix is ​​used to describe the change in polarization when light passes through the designed system. The Stokes vector expression is as follows: S = [S0, S1, S2, S3] T , S0 represents the total light intensity, that is, the sum of the horizontal polarization component and the vertical polarization component, S1 represents the difference between the horizontal polarization component and the vertical polarization component, S2 represents the difference between the 45° and 135° polarization components, and S3 represents the difference between the right-hand circular polarization component and the left-hand circular polarization component.

[0004] The Mueller matrix has the following form:

[0005]

[0006] The Mueller matrix is ​​the transformation matrix between the incident Stokes vector and the outgoing Stokes vector, satisfying the following formula: out =MS in , where S in represents the Stokes vector of the incident light, S out Represents the Stokes vector of the outgoing light.

[0007] In order to conduct relevant analysis on pathological tissue, one method is to detect the optical information of pathological tissue by polarization imaging technology. And this is also a widely used method at present. For example, polarization imaging is used to help radiofrequency ablation in the treatment of arrhythmia symptoms, and imaging technology is used to accurately determine the scope of radiofrequency damage. Polarization imaging is used to determine the scope of healthy tissue and cancerous tissue in the colon and cervix. Polarization imaging is used to measure glucose levels in turbid media. In addition to providing structural and morphological information, polarization imaging also provides polarization information of collagen tissue, including depolarization, linear delay and optical rotation. Therefore, using polarization imaging to measure the Mueller matrix information of collagen tissue becomes a feasible means.

[0008] At present, polarization spatial frequency imaging, which combines spatial frequency imaging and polarization imaging technology, is being studied in depth. For example, Bin Yang et al. designed a polarization spatial frequency system device to detect the fiber direction of bovine tendon tissue and achieved good experimental results. WILL GOTH designed a similar device and detected the collagen fiber arrangement in the valve of pig heart valve. Samuel V. Jett et al. further made a quantitative analysis of the fiber arrangement of mitral valve leaflet tissue collagen under mechanical load and also measured some Mueller matrix information.

[0009] However, their experimental setup has some shortcomings. They used polarization spatial frequency domain imaging, and their experimental setup is as follows Figure 3 and Figure 4 As shown. It mainly consists of a digital micromirror chip (DMD), a bandpass filter, a lens, a polarizer and an industrial CCD camera. The structured light generated by the light source passes through the DMD, and the stripe light reflected by the polarizer is converted into polarized light, which is irradiated onto the sample to be tested. The reflected light is scattered on the sample to be tested, and then passes through the polarizer and is detected by the industrial CCD camera to detect the light intensity. During the measurement process, the polarizer rotates. The output light intensity is measured every time the angle is changed. Different output light intensities correspond to different equations about the elements of the Mueller matrix. Since the Mueller matrix has 16 elements, that is, 16 unknowns need to be solved, it is necessary to rotate and change the angle at least 16 times to achieve 16 polarization combinations to obtain the Mueller matrix of the sample. In the experimental measurement, the polarizer system and the analyzer system share a set of polarizers, and the polarization state range of the polarized light provided is small. Only the polarization state of linear polarized light is considered, and the influence of circular polarized light and other polarization states is not considered, which is insufficient for measuring the integrity of the Mueller matrix of the biological tissue to be tested. Summary of the invention

[0010] The purpose of the present invention is to provide a new Mueller matrix measurement system and method, which can efficiently and accurately measure the complete Mueller matrix of a target.

[0011] The present invention solves the above technical problems through the following technical solutions:

[0012] A Mueller matrix measurement system comprises: a light source system (11), a polarizing subsystem (12), a sample stage to be measured (13), and an analyzing subsystem (14); the light source system (11) comprises: a light source (111), a lens (112), and a bandpass filter (113); the polarizing subsystem (12) comprises: a digital micro-mirror (121), a first vertical linear polarizing plate (P1), a first phase retarder (LCVR1), a second phase retarder (LCVR2), a first imaging lens (L1), and a first reflecting mirror (122); the analyzing subsystem (14) comprises: a second reflecting mirror (141), a third phase retarder (LCVR3), a fourth phase retarder (LCVR4), a second vertical linear polarizing plate (P2), a second imaging lens (L2), and a camera (142);

[0013] The light source (111) emits modulated light vertically upward, and generates modulated light of a single wavelength after passing through a lens (112) and a bandpass filter (113). The digital micro-reflector (121) reflects the modulated light of the single wavelength horizontally. A first vertical linear polarizer (P1), a first phase delay plate (LCVR1), a second phase delay plate (LCVR2), a first imaging lens (L1), and a first reflector (122) are sequentially arranged from left to right along the optical path of the horizontal modulated light. The digital micro-reflector (121) is loaded with a stripe image. The first vertical linear polarizer (P1) is used to convert the incident modulated light into linearly polarized light. The first phase delay plate (LCVR1) and the second phase delay plate (LCVR2) are sequentially arranged from left to right. The invention discloses a method for transmitting the linear polarization state of a horizontally polarized light to a sample stage (13) and a first reflector (122). The method comprises: transmitting the linear polarization state of a horizontally polarized light to a sample stage (13) and a first reflector (141). The linear polarized light with the stripe pattern is projected onto the surface of the biological tissue to be tested placed on the sample stage (13) after the horizontally modulated light passes through the first vertical linear polarizer (P1), the first phase delay plate (LCVR1), the second phase delay plate (LCVR2), and the first imaging lens (L1). The linear polarized light with the stripe pattern is scattered in the biological tissue to be tested, and the scattered light is reflected by the second reflector (141) and then emitted horizontally. The scattered light then passes through the third phase delay plate (LCVR3), the fourth phase delay plate (LCVR4), the second vertical linear polarizer (P2), and the second imaging lens (L2) in sequence, and is then captured by the camera (142).

[0014] The light source system (11) of the Mueller matrix measurement system of the present invention emits modulated light vertically upward, and the first vertical linear polarizer (P1) is used to convert the incident modulated light into linear polarized light; the first phase delay plate (LCVR1) and the second phase delay plate (LCVR2) modulate the polarization state of the linear polarized light, the digital micro-reflector (121) is loaded with a stripe image, and the linear polarized light with the stripe image is scattered in the biological tissue to be measured, and the scattered light passes through the third phase delay plate (LCVR3), the first phase delay plate (143), and the second vertical linear polarizer (P2) in sequence, and is captured by the camera (142); the polarization state of the modulated linear polarized light is controlled by the first phase delay plate (LCVR1), the second phase delay plate (LCVR2), the third phase delay plate (LCVR3), and the fourth phase delay plate (LCVR4), so as to control the measurement depth of the polarized light on the biological tissue to be measured, thereby improving the calculation accuracy of the light intensity value of the emitted light, thereby improving the accuracy of calculating the Mueller matrix.

[0015] In one embodiment, the fast axes of the first phase retarder (LCVR1) and the second phase retarder (LCVR2) are at angles of 45° and 90° to the horizontal direction, respectively.

[0016] In one embodiment, the fast axes of the third phase retarder (LCVR3) and the fourth phase retarder (LCVR4) are angled with the horizontal direction at 90° and 45° respectively.

[0017] In one embodiment, the light source system (11) adopts a composite light source.

[0018] In one embodiment, the camera (142) is an industrial-grade CCD camera.

[0019] A measurement method applied to the Mueller matrix measurement system comprises the following steps:

[0020] S1, calculating the spatial frequency of the fringe image according to the imaging depth of the sample to be tested;

[0021] S2, according to the spatial frequency calculated in step S1, selecting three fringe images with different phases at the spatial frequency, and loading each fringe image into the digital micro-reflector (121);

[0022] S3, using the polarization subsystem (12) to perform four polarization state modulations, and the polarization detection subsystem (14) to perform four modulations, and combining them in pairs to obtain 16 groups of different polarization state combinations;

[0023] S4, projecting the three fringe images with different phases for each polarization state combination, respectively, to obtain the light intensity values ​​of scattered light under 16 polarization state combinations, and representing the light intensity value of scattered light under each polarization state combination with a Stokes vector;

[0024] S5, the Stokes vector of the intensity value of the scattered light under each group of polarization state combination is expressed as the product of the Mueller matrix of the polarization analyzer subsystem (14), the Mueller matrix of the sample, and the Mueller matrix of the polarizing subsystem (12), and a matrix equation is obtained by taking the total intensity value element of the Stokes vector of the intensity value of the scattered light under each group of polarization state combination, that is, the first element in the Stokes vector;

[0025] S6. Repeat step S5 to obtain 16 sets of matrix equations in total. By solving the 16 sets of matrix equations, the values ​​of the 16 elements in the Mueller matrix of the sample to be tested are obtained.

[0026] Furthermore, the formula for calculating the spatial frequency of the fringe image according to the imaging depth of the sample to be tested in step S1 is as follows:

[0027]

[0028] Among them, depth is the fixed imaging depth, u a is the absorption coefficient of the sample to be tested, u s ' is the scattering coefficient of the sample to be tested, f x is the spatial frequency of the fringe image.

[0029] In one embodiment, the phases of the three fringe images with different phases in step S2 are: 0°, 120°, and 240°.

[0030] Furthermore, the Stokes vector of the intensity value of the scattered light under each polarization state combination described in step S5 is expressed as the product of the Mueller matrix of the polarization analyzer subsystem (14), the Mueller matrix of the sample to be tested, and the Mueller matrix of the polarizing subsystem (12) in the following form:

[0031] I Out =M P2 *M LCVR4 *M LCVR3 *M Sample *M LCVR2 *M LCVR1 *M P1 *I in

[0032] Among them, I Out is the Stokes vector of the scattered light intensity value under each polarization state combination, M P2 is the Mueller matrix of the second vertical linear polarizer (P2) of the polarization analyzer subsystem (14), M LCVR4 and M LCVR3are the Mueller matrices of the fourth phase delay plate (LCVR4) and the third phase delay plate (LCVR3) of the polarization analysis subsystem (14), M Sample is the Mueller matrix of the sample to be tested, M LCVR2 and M LCVR1 are the Mueller matrices of the second phase retarder (LCVR2) and the first phase retarder (LCVR1) of the polarizing subsystem (12), M P1 is the Mueller matrix of the first vertical linear polarizer (P1) of the polarizing subsystem (12), I in is the Stokes vector of the incident light of the light source system (11).

[0033] The advantages of the present invention are:

[0034] The present invention provides a Mueller matrix measurement system, wherein a light source system (11) emits modulated light vertically upward, a first vertical linear polarizer (P1) is used to convert incident modulated light into linearly polarized light; a first phase delay plate (LCVR1) and a second phase delay plate (LCVR2) modulate the polarization state of the linearly polarized light; a digital micro-reflector (121) is loaded with a stripe image, the linearly polarized light with the stripe image is scattered in a biological tissue to be measured, and the scattered light passes through a third phase delay plate (LCVR3), a first phase delay plate (143), and a second vertical linear polarizer (P2) in sequence before being captured by a camera (142); the polarization state of the modulated linearly polarized light is controlled by the first phase delay plate (LCVR1), the second phase delay plate (LCVR2), the third phase delay plate (LCVR3), and the fourth phase delay plate (LCVR4), so as to control the measurement depth of the polarized light on the biological tissue to be measured, thereby improving the calculation accuracy of the light intensity value of the emitted light, thereby improving the accuracy of calculating the Mueller matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a structural diagram of a Mueller matrix measurement system according to an embodiment of the present invention;

[0036] Figure 2 is a control flow chart of a Mueller matrix measurement system according to an embodiment of the present invention;

[0037] Figure 3 It is a schematic diagram of the wave plate rotation method;

[0038] Figure 4 This is a schematic diagram of traditional polarization spatial frequency domain imaging. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0041] Embodiment 1

[0042] like Figure 1 As shown, a Mueller matrix measurement system comprises: a light source system (11), a polarizing subsystem (12), a sample stage to be measured (13), and an analyzing subsystem (14); the light source system (11) comprises: a light source (111), a lens (112), and a bandpass filter (113); the polarizing subsystem (12) comprises: a digital micro-reflector (121), a first vertical linear polarizer (P1), a first phase retarder (LCVR1), a second phase retarder (LCVR2), a first imaging lens (L1), and a first reflector (122); the analyzing subsystem (14) comprises: a second reflector (141), a third phase retarder (LCVR3), a fourth phase retarder (LCVR4), a second vertical linear polarizer (P2), a second imaging lens (L2), and a camera (142).

[0043] The light source (111) emits modulated light vertically upward, and generates modulated light of a single wavelength after passing through a lens (112) and a bandpass filter (113). The light source system (11) may use a composite light source. The digital micro-reflector (121) reflects the modulated light of a single wavelength horizontally. A first vertical linear polarizer (P1), a first phase delay plate (LCVR1), a second phase delay plate (LCVR2), a first imaging lens (L1), and a first reflector (122) are sequentially arranged along the optical path of the horizontal modulated light from left to right. The digital micro-reflector (121) is loaded with a stripe image. The first vertical linear polarizer (P1) is used to convert the incident modulated light into linearly polarized light. The first phase delay plate (LCVR1) and the second phase delay plate (LCVR2) are used to modulate the polarization state of the linearly polarized light. The fast axes of the first phase delay plate (LCVR1) and the second phase delay plate (LCVR2) are at angles of 45° and 90° to the horizontal direction, respectively. The horizontal modulated light passes through the first vertical linear polarizer (P1), the first phase delay plate (LCVR1), and the second phase delay plate (LCVR2). The invention relates to a method for producing a linear polarized light beam having a stripe pattern, wherein the linear polarized light beam passes through a first reflector (122), a second phase retarder (LCVR1), a second phase retarder (LCVR2), and a first imaging lens (L1), and then projects the linear polarized light beam with a stripe pattern onto the surface of the biological tissue to be tested placed on the sample stage (13) to be tested; the linear polarized light beam with the stripe pattern is scattered in the biological tissue to be tested, and the scattered light beam is reflected by the second reflector (141) and then emitted horizontally, and then sequentially passes through a third phase retarder (LCVR3), a fourth phase retarder (LCVR4), a second vertical linear polarizer (P2), and a second imaging lens (L2), and then is captured by a camera (142); the fast axes of the third phase retarder (LCVR3) and the fourth phase retarder (LCVR4) have angles of 90° and 45° with the horizontal direction, respectively; and the camera (142) adopts an industrial-grade CCD (charge coupled device) camera.

[0044] like Figure 2 As shown, a Mueller matrix measurement system of the present invention controls the voltages of the first phase delay plate (LCVR1), the second phase delay plate (LCVR2), the third phase delay plate (LCVR3), and the fourth phase delay plate (LCVR4) by a set of customized QT programs, and controls the stripe loading of the DMD and the imaging of the camera. It is easier to operate the polarization state of polarized light than the traditional wave plate, and the change of the polarization state of the structured light can be achieved only by loading the voltage. It is more accurate than manually adjusting the wave plate, and the modulation range of the polarization state of polarized light is wider, so that the complete Mueller matrix of the biological tissue to be measured can be measured, making the calculated Mueller matrix more accurate.

[0045] The measurement method is as follows:

[0046] 1. Determine the spatial frequency of the fringe image

[0047] In experimental measurements, it is necessary to measure the epidermis of biological tissues. Therefore, it is necessary to determine the spatial frequency f of the fringe image at the imaging depth of the epidermis. x The spatial frequency imaging method is used to perform three measurements (the spatial frequency imaging method is an existing method, see the literature: Gioux S, Mazhar A, Cuccia DJ. Spatial frequency domain imaging in 2019: principles, applications, and perspectives). In each measurement, a different fringe image is projected. The light and dark stripes of the pattern are periodically transformed in the form of trigonometric functions. The phases of the fringe images are 0°, 120°, and 240°, respectively.

[0048] Assume that the function expression of the incident light intensity incident on the sample to be tested is:

[0049]

[0050] Among them, s0, M0, f x ,x, They are the light intensity of the light source, the spatial modulation depth, the spatial frequency of the fringe image, the spatial coordinates, and the spatial phase.

[0051] During the measurement, the structured light is scattered in the sample tissue and the scattered image is captured by the detection camera. The scattered light intensity I(x,f x ) can be decomposed into a DC component I DC (x) and the AC component I AC (x,f x ).

[0052] I(x,f x )=I DC (x)+I AC (x,f x ) (2)

[0053] DC Component I DC Only related to the spatial position x, the AC component I AC is the spatial position x and the spatial frequency f x The function has the following expression:

[0054]

[0055] M ACRepresents the amplitude of the reflected photon density. It is generally solved using the three-phase shift method. During the measurement, three fringe images are projected, and the light intensity values ​​of the three images represent I0(x,f x ),I 120 (x,f x ),I 240 (x,f x ). There are the following expressions:

[0056]

[0057] There is also a DC component I DC (x,f x )expression:

[0058]

[0059] After calculating the above components, use the same steps to measure the relevant components of the diffuse reflector. Then the diffuse reflectance Rd of the sample tissue can be expressed as:

[0060]

[0061] The denominator is the AC component of the diffuse reflector, R d,ref (x,f x ) is the diffuse reflectance of the diffuse reflection plate (0.99).

[0062] According to the diffuse reflection approximation theory, the diffuse reflectance, spatial frequency, absorption coefficient, and scattering coefficient have the following expressions:

[0063]

[0064] Where A is a constant, u tr =u a +u s '.u a is the absorption coefficient, u s ' is the scattering coefficient. Therefore, the spatial frequency fx is the independent variable and Rd is the dependent variable in the whole expression. By fitting different spatial frequencies and corresponding diffuse reflectance using the least squares method, the absorption coefficient and scattering coefficient can be obtained.

[0065] After the absorption coefficient and scattering coefficient are obtained, the imaging depth, absorption coefficient, scattering coefficient, and spatial frequency have the following expressions.

[0066]

[0067] By setting the imaging depth, the spatial frequency f of the fringe image can be determined x , and then proceed to the measurement in step 2.

[0068] 2. Use the Mueller matrix measurement system to measure 16 groups of polarization state combinations

[0069] Since the Mueller matrix has 16 elements, the polarized light needs to be modulated in 16 different polarization states during the entire measurement. Therefore, the polarization system needs to be modulated in polarization state 4 times (by loading different voltages on the liquid crystal phase retarder), and the polarization analyzer system needs to be modulated 4 times. By combining two by two, 16 different polarization state combinations can be obtained. And because the spatial frequency imaging method is used, three fringe images need to be projected. Therefore, under one polarization state modulation, the biological tissue to be measured needs to be imaged three times to obtain the final light intensity value result. That is, the polarization system confirms one polarization state, and the polarization analyzer system confirms one polarization state. Under this polarization state combination condition, three fringe images are projected in sequence to obtain three imaging pictures. Repeat the above steps to measure the remaining 15 groups of polarization state combinations, and obtain a total of 16 groups of imaging results under polarization state combinations, totaling 48 imaging pictures.

[0070] 3. Preparation for Mueller matrix calculation

[0071] According to step 1, the intensity values ​​of scattered light under 16 groups of polarization states are calculated.

[0072] I out (x,f x )=I DC (x,f x )+I AC (x,f x ) (9)

[0073] according to Figure 1 As shown, the Stokes vector I of the outgoing light detected by the CCD after being reflected by the target out (x,f x ) can be expressed as:

[0074] I Out =M P2 *M LCVR4 *M LCVR3 *M Sample *M LCVR2 *M LCVR1 *M P1 *I in (10)

[0075] Among them, I in is the Stokes vector of the incident light, M P1 is the Mueller matrix of the vertical polarizer in the polarizing system, M LCVR1 and M LCVR2 are the Mueller matrices of the liquid crystal phase retarders LCVR1 and LCVR2, M Sample is the Mueller matrix of the biological tissue to be tested, MLCVR4 and M LCVR3 are the Mueller matrices of the liquid crystal phase retarders LCVR4 and LCVR3, M P2 is the Mueller matrix of the vertical polarizer in the analyzer system.

[0076] During the measurement of step 2, the angles between the fast axes of LCVR1 and LCVR2 and the horizontal direction are 45° and 90° respectively (LCVR4 and LCVR3 are also 45° and 90°). Since the incident light is modulated by a vertical linear polarizer, the incident Stokes vector I in =[1,-1,0,0] T .

[0077] Therefore, the Stokes vector I of the light emitted from LCVR2 LCVR2 It can be expressed as:

[0078]

[0079] Wherein, δ1 and δ2 are phase delays of two liquid crystal phase retarders respectively, which are determined by the loading voltage set on the liquid crystal phase retarders.

[0080] Substitute (11) into (10) and let M Pi =M P2 *M LCVR4 *M LCVR3 We can get:

[0081]

[0082] In step 2, the loading voltage of the liquid crystal phase retarder of the polarization analyzer system is set to make the polarization analyzer system perform four polarization state modulations respectively.

[0083] M LCVR4 , M LCVR3 The Mueller matrix of the liquid crystal phase retarders LCVR1 and LCVR2 in the polarizing system is the same and is determined by the applied voltage. The Mueller matrix of the vertical polarizer can also be calculated, so it is M Pi Knowable.

[0084]

[0085] Among them, δ1′ and δ2′ are the phase delays of two liquid crystal phase retarders respectively;

[0086] Take I separately Out The first number (total light intensity value), that is, only calculate M Pi The first line of , then:

[0087]

[0088]

[0089] Where a is a coefficient determined by δ1, δ2, δ1′ and δ2′, and the value is different for each set of measurements. A total of 16 sets of data are measured, and 16 sets of equations can be obtained: I = A*M. The final Mueller matrix can be obtained by solving the matrix equation.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Mueller matrix measurement method based on a Mueller matrix measurement system, characterized in that: The Mueller matrix measurement system comprises: a light source system (11), a polarizing subsystem (12), a sample stage to be measured (13), and an analyzing subsystem (14); the light source system (11) comprises: a light source (111), a lens (112), and a bandpass filter (113); the polarizing subsystem (12) comprises: a digital micro-mirror (121), a first vertical linear polarizer (P1), a first phase retarder (LCVR1), a second phase retarder (LCVR2), a first imaging lens (L1), and a first reflecting mirror (122); the analyzing subsystem (14) comprises: a second reflecting mirror (141), a third phase retarder (LCVR3), a fourth phase retarder (LCVR4), a second vertical linear polarizer (P2), a second imaging lens (L2), and a camera (142); The light source (111) emits modulated light vertically upward, and generates modulated light of a single wavelength after passing through a lens (112) and a bandpass filter (113). The digital micro-reflector (121) reflects the modulated light of the single wavelength horizontally. A first vertical linear polarizer (P1), a first phase delay plate (LCVR1), a second phase delay plate (LCVR2), a first imaging lens (L1), and a first reflector (122) are sequentially arranged from left to right along the optical path of the horizontal modulated light. The digital micro-reflector (121) is loaded with a stripe image. The first vertical linear polarizer (P1) is used to convert the incident modulated light into linearly polarized light. The first phase delay plate (LCVR1) and the second phase delay plate (LCVR2) are sequentially arranged from left to right. CVR2) is used to modulate the polarization state of linear polarized light; after the horizontal modulated light passes through the first vertical linear polarizer (P1), the first phase delay plate (LCVR1), the second phase delay plate (LCVR2), and the first imaging lens (L1), the first reflector (122) projects the linear polarized light with the stripe image onto the surface of the biological tissue to be tested placed on the sample stage (13) to be tested; the linear polarized light with the stripe image is scattered in the biological tissue to be tested, the scattered light is reflected by the second reflector (141) and then emitted horizontally, and then passes through the third phase delay plate (LCVR3), the fourth phase delay plate (LCVR4), the second vertical linear polarizer (P2), and the second imaging lens (L2) in sequence, and is captured by the camera (142); The measuring method comprises the following steps: S1, calculating the spatial frequency of the fringe image according to the imaging depth of the sample to be tested; S2, according to the spatial frequency calculated in step S1, selecting three fringe images with different phases at the spatial frequency, and loading each fringe image into the digital micro-reflector (121); S3, using the polarization subsystem (12) to perform four polarization state modulations, and the polarization detection subsystem (14) to perform four modulations, and combining them in pairs to obtain 16 groups of different polarization state combinations; S4, projecting the three fringe images with different phases for each polarization state combination, respectively, to obtain the light intensity values ​​of scattered light under 16 polarization state combinations, and representing the light intensity value of scattered light under each polarization state combination with a Stokes vector; S5, the Stokes vector of the intensity value of the scattered light under each group of polarization state combination is expressed as the product of the Mueller matrix of the polarization analyzer subsystem (14), the Mueller matrix of the sample, and the Mueller matrix of the polarizing subsystem (12), and a matrix equation is obtained by taking the total intensity value element of the Stokes vector of the intensity value of the scattered light under each group of polarization state combination, that is, the first element in the Stokes vector; S6. Repeat step S5 to obtain 16 sets of matrix equations in total. By solving the 16 sets of matrix equations, the values ​​of the 16 elements in the Mueller matrix of the sample are obtained.

2. The measuring method according to claim 1, characterized in that: The formula for calculating the spatial frequency of the fringe image according to the imaging depth of the sample to be tested in step S1 is as follows: Among them, depth is the fixed imaging depth, u a is the absorption coefficient of the sample to be tested, u s ' is the scattering coefficient of the sample to be tested, f x is the spatial frequency of the fringe image.

3. The measuring method according to claim 1, characterized in that: The phases of the three fringe images with different phases described in step S2 are: 0°, 120°, and 240° respectively.

4. The measuring method according to claim 2, characterized in that: The Stokes vector of the intensity value of the scattered light under each polarization state combination described in step S5 is expressed as the product of the Mueller matrix of the polarization analyzer subsystem (14), the Mueller matrix of the sample, and the Mueller matrix of the polarizing subsystem (12) in the following form: I Out =M P2 *M LCVR4 *M LCVR3 *M Sample *M LCVR2 *M LCVR1 *M P1 *I in Among them, I Out is the Stokes vector of the scattered light intensity value under each polarization state combination, M P2 is the Mueller matrix of the second vertical linear polarizer (P2) of the polarization analyzer subsystem (14), M LCVR4 and M LCVR3 are the Mueller matrices of the fourth phase delay plate (LCVR4) and the third phase delay plate (LCVR3) of the polarization analysis subsystem (14), M Sample is the Mueller matrix of the sample to be tested, M LCVR2 and M LCVR1 are the Mueller matrices of the second phase retarder (LCVR2) and the first phase retarder (LCVR1) of the polarizing subsystem (12), M P1 is the Mueller matrix of the first vertical linear polarizer (P1) of the polarizing subsystem (12), I in is the Stokes vector of the incident light of the light source system (11).

5. The measuring method according to claim 1, characterized in that: The fast axes of the first phase retarder (LCVR1) and the second phase retarder (LCVR2) have angles of 45° and 90° with the horizontal direction respectively.

6. The measuring method according to claim 1, characterized in that: The fast axes of the third phase retarder (LCVR3) and the fourth phase retarder (LCVR4) are at angles of 90° and 45° to the horizontal direction respectively.

7. The measuring method according to claim 1, characterized in that: The light source system (11) adopts a composite light source.

8. The measuring method according to claim 1, characterized in that: The camera (142) is an industrial-grade CCD camera.

Images